The purpose of this project is to establish a system for simultaneous assay of in vitro malignant transformation and mutation of human and mouse cells by chemical and physical carcinogens. The assay system for mutation induced by ultraviolet light has been established using human diploid fibroblast and BALB 3T3 subclone cells as target cells and ouabain-resistance as a marker of mutation. Combined with the transformation assay system that has been previously established in this laboratory using the same cell system, it is now possible to study comparatively the induction of transformation and mutation in the same population of the cultured human and mouse cells.